Mycoplasma pneumoniae causes atypical pneumonia and, on rare occasions, cold agglutinin-mediated hemolytic anemia. The cold agglutinins in M. pneumoniae infection are directed against which red blood cell antigen?
- A I antigen (a branched polysaccharide on adult red blood cells) ✓
- B P antigen (globoside)
- C Duffy antigen (Fy)
- D MNS antigen (sialoglycoprotein A)
Correct answer: A. I antigen (a branched polysaccharide on adult red blood cells)
Explanation
M. pneumoniae surface glycolipids share antigenic similarity with the I antigen of human red blood cells. Polyclonal IgM antibodies produced against M. pneumoniae cross-react with RBC I antigen, particularly at cooler peripheral temperatures (4°C), causing agglutination — hence 'cold agglutinins.' These anti-I IgM antibodies activate complement at warmer core temperatures as blood recirculates, causing extravascular hemolysis. Cold agglutinin titer ≥1:64 in the appropriate clinical context supports M. pneumoniae infection.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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